This application is a U.S. National Phase application of PCT International application PCT/JP99/05529.
The present invention concerns a method for manufacturing an electrode and an electrode used for batteries, etc. such as nickel hydrogen battery, nickel cadmium battery, etc., and an apparatus for forming an electrode for a battery constructed by spirally winding a porous metallic supporting base filled with active material, and an electrode manufacturing by this processing method.
The electrode of a secondary battery comprises foamed metal having continuous 3-dimensional network structure highly porous as supporting base and active material filled in this foamed metal. An electrode having such construction demonstrates comparatively excellent discharge characteristics. Moreover, these days, there is a strong request for improvement of high-efficiency discharge characteristics. To achieve that objective, the following construction is proposed: The manufacturing method comprises a process of forming a portion in which the core material portion is exposed without filling active material on one side along the longitudinal direction of the electrode, and a process of forming an about cylindrical electrode group by spirally winding positive and negative electrodes placed one upon another alternately, through a separator, and the end face of said about cylindrical electrode group is constructed only with the core material portion not filled with active material. By this construction, an exposed portion of a metal suitable for welding is formed and, by tabless system, the lead piece is welded to this exposed portion of metal. A secondary battery is proposed for the collecting characteristics of which are improved by such construction.
However, an electrode using foamed metal as core material does not have any solid metallic part in the core portion to which the lead piece can be directly welded. As countermeasures for it are proposed a method of further providing a metal sprayed layer on one side of the electrode on which to weld the lead piece, a method of depositing metal foil in advance for reinforcement, etc., to improve the electric conductivity of the material core portion. Moreover, in the Japanese Patent Laid-Open Publication No. 139251/87 is disclosed a method in which the portion not filled with active material in the electrode core material using foamed metal sheet is compressed in the direction of breadth of the electrode, as a measure for reinforcing the lead piece welding portion of the core material. By this method, the density and strength of the metallic part are increased, enabling welding of the lead piece.
This conventional method is indicated in FIG. 7. The entire surface of the slender and rectangular electrode material 51 is pinched from both the left and the right sides by flat plane, and a strong pressurizing force F1 is applied to that surface by an air cylinder 52. While preventing production of any deformation such as bend, unevenness, change of thickness, etc. on the surface of the electrode and in the state in which one side of the electrode material 51 is supported from below, a strong pressurizing force P is applied by using a press 53, in the direction of breadth of the electrode, from the side of the electrode material not filled with active material. The portion not filled with active material of the foamed metal forming one side in longitudinal direction of the electrode material 51 is compressed, to crush the voids produced with foaming. By this method, the density and strength of the metallic part in one side not filled with active material of the electrode material 51 are increased. In this way, attempts were made for achieving easy welding and improvement of quality.
However, generally, the filling volume of active material is variable depending on the portions of the surface of electrode and, therefore, the thickness of the surface of electrode is uneven. For that reason, it was difficult to uniformly support the surface of the electrode with metallic plane of high hardness from both sides of the electrode material. Moreover, variations were produced also in the filling width of active material in longitudinal direction of the electrode material 51. For that reason, the supporting state of the electrode material changes at the portion in longitudinal direction and, when an attempt is made to apply a uniform pressurizing force in the longitudinal direction of the electrode material with a press, both the state of the electrode material receiving the pressurizing force of the press and the supporting state of the electrode material change. As a result, variations were liable to be produced in the strength and density of the side of electrode serving as lead welding portion, thus making it difficult to manufacture electrodes fully satisfactory from the viewpoint of quality. In the case where priority is given to increasing the strength and density of the lead welding portion of the electrode material by increasing the pressurizing force P of the press applied in the direction of breadth of the electrode material 51, the pressurizing force has influences on the entire breadth of the electrode and the breadth of electrode tends to get narrower on the entire length, and the electrode is deformed under a strong pressurizing force applied locally. It was therefore difficult to form a lead welding portion of high density suitable for welding with a narrow width locally, only on one side of the breadth of electrode over the entire length of the electrode material. Furthermore, it was also difficult to fully retain excellent characteristics of foamed metal in other portions. Still more, this conventional method was insufficient particularly in productivity, and was therefore far from satisfactory.
In the conventional art described above, it was difficult to form any high-density lead welding portion suitable for welding of tabless lead uniformly and with high quality, over the entire length of one side in longitudinal direction of the electrode material, because the filling condition of active material in the electrode material produces variations by delicately changing locally. In addition, when a high-grade plasticity processing is applied to the foamed metal, as described above, the foamed metal is crushed, and the high-density foamed metal portion gets hard and fragile. For that reason, this conventional method also presents a defect that, in a subsequent process, fissures and cracks are produced when forming a cylindrical shape by spirally winding the positive and negative pole plates one upon another through a separator.
The Japan abstract J 57 80672 discloses the manufacturing of an electrode plate for alkaline batteries. A metal fibre substrate of rectangular form having a main area and an end section extending in the lengthwise direction and not being filled with active material. This strip like end section being folded in two or more plies. After this folding step the folded section is compressed to decrease the thickness thereof by applying a force to the folded section.
The object of the present invention is to provide an electrode enabling improvement of both battery performances and productivity in the processes for manufacturing an electrode, a method for manufacturing an electrode and an apparatus for manufacturing an electrode.
These objects are achieved with respect to a method for manufacturing an electrode by the features of claim 1, to an apparatus for forming an electrode by the features of claim 6, and to an electrode for a battery by the features of claim 12, respectively.
Advantageous developments are claimed by the dependent claims.
A manufacturing method of electrode according to the present invention comprises:
(a) a step of filling active material in foamed metal having voids and supplying electrode material having filled portion filled with active material, unfilled portion not filled with the active material, and a boundary line between the filled portion and the unfilled portion, in which the electrode material has a rectangular or band-like shape, the unfilled portion is formed along a longer side of the electrode material, and the boundary line has an about straight line parallel to the longer side,
(b) a step of bending part of the unfilled portion, in parallel to the boundary line passing through the unfilled portion, and at right angle against the filled portion, and
(c) a step of forming a lead welding portion along the direction of the longer side, by applying, to the unfilled portion bent, a force in the direction perpendicular to the filled portion in a way to crush said voids, and compressing said bent part.
Particularly preferably, in the step (c), the height of said unfilled portion is compressed to a thickness no more than about the thickness of the filled portion.
In the manufacturing apparatus for forming electrode from electrode material bent at right angle according to the present invention, the electrode material is in the shape of a rectangle having filled portion in which active material is filled in foamed metal having voids and unfilled portion not filled with the active material, and the electrode material has the bent portion in which part of the unfilled portion is bent at right angle against the filled portion, in parallel to the longer side of the rectangle passing through the unfilled portion.
The manufacturing apparatus according to the present invention comprises a first roller and a second roller which are installed in parallel with each other at the shaft center and turn in directions opposite to each other, and a guide bar installed between the first roller and the second roller. The distance between the outer circumference of the first roller and the outer circumference of the second roller is equal to the thickness of said filled portion. The filled portion of the electrode material is sent between the outer circumferential face of the first roller and the outer circumferential face of the second roller, the bent portion is sent between the side face of the second roller, and the guide bar and, when passing through the narrowest area between the first roller and the second roller, the bent portion is compressed in the direction perpendicular to the filled portion, the voids in the foamed metal in the bent portion are crushed, and a high-density lead welding portion is formed along the direction of the longer side.
Particularly preferably, the second roller is a stepped roller having a first outer circumferential face, a second outer circumferential face, a third outer circumferential face and a fourth outer circumferential face.
The second outer circumferential face and the third outer circumferential face are positioned between the first outer circumferential face and the fourth outer circumferential face, and the second outer circumferential face is positioned on the first outer circumferential face side.
Of the first outer circumferential face, the second outer circumferential face, the third outer circumferential face and the fourth outer circumferential face, the first outer circumferential face has the largest outside diameter, the second outer circumferential face and the fourth outer circumferential face have one same outside diameter with each other, and the third outer circumferential face has the smallest outside diameter.
The side face of the second roller is formed by the wall face of stepped portion between the first outer circumferential face and the second outer circumferential face.
The guide bar is installed in small clearance with the third outer circumferential face.
The bent portion is sent to be positioned between the side face of said second roller and the guide bar.
The bent portion is compressed by the second outer circumferential face of the second roller and the outer circumferential face of the first roller.
The electrode for battery according to the present invention comprises filled portion having active material filled in foamed metal, and lead welding portion formed by compression of the foamed metal which does not contain the active material. The foamed metal has voids. The lead welding portion is a metallic portion formed with crushing of the voids, by compressing the bent portion formed by bending the unfilled portion not having active material at right angle against the filled portion reducing the height of the folded portion.
Particularly preferably, both the lead welding portion and the filled portion are in the shape of a rectangle, and the lead welding portion has a width narrower than that of the filled portion.
Particularly preferably, the electrode has a shape wound, through a separator, in the direction of the longer side of the rectangle.
Particularly preferably, on a least one face of the surface and the back face of the lead welding portion is formed a plurality of up-down patterns.
This construction makes it possible to obtain, as lead welding portion, a metallic portion having high density and high mechanical strength. In the case where a lead wire is connected to this metallic portion which is a lead welding portion, it becomes possible to perform direct welding of a tabless lead wire to the end face of an electrode, which was difficult with the conventional method. Moreover, by providing a plurality of groove-shaped ups and downs in the lead welding portion, it becomes possible to prevent production of cracks, when placing positive and negative electrode plates one upon another, through a separator, and spirally winding them up to form a cylindrical shape.
As described above, with the construction of the present invention, it becomes possible to obtain a manufacturing method and a manufacturing apparatus of electrode for battery, much simpler and less expensive compared with the conventional manufacturing apparatus, and an electrode.